Various techniques have been attempted for efficient placement of interconnections in order to increase the degree of integration of semiconductor devices in accordance with the thinning and shortening of electronic devices. The interconnections include a plurality of horizontal interconnections and a plurality of contact plugs connected to the horizontal interconnections. Minimizing the spacing of the plurality of contact plugs is advantageous for high integration of semiconductor devices. The plurality of contact plugs should be insulated from each other. There is a need for a new technique for securing insulation from adjacent contact plugs and minimizing spacing between the contact plugs.